Most digital electronic systems use one or more clock signals to control their operation. It is not uncommon for a digital system to use multiple clock groups. A clock tree may have multiple and different frequencies. Each frequency or the tree as whole also may have special requirements such as maximum jitter, holdover, spread spectrum, instant on (comes on with no programming), and many other requirements.
Clocking devices typically contain a source frequency which is divided down by dividers in order to generate additional frequencies. For some clock trees, these frequencies might all nicely divide into a single frequency that can be generated by a source such as a VCO (Voltage Controlled Oscillator) of a device, while others might require multiple sources. Finding the right combination of devices and the best way to configure such devices is often time consuming and overwhelming due to the availability of a multitude of clock parts.